1. Field of the Invention
The present invention relates generally to suspension systems for vehicles. Specifically, the invention relates to the attachment of spring assemblies to a vehicle chassis, such as to the frame of a trailer. A spring hanger and a method of attaching the same are disclosed.
2. Description of the Prior Art
Trailer suspensions are almost exclusively manufactured as a separate component that is subsequently attached to the trailer chassis during assembly. Suspension systems are well known in the art, as are hangers for attaching suspension components such as springs or leaf springs to a vehicle or trailer chassis. Suspensions may be attached with bolts or other fasteners, but on steel framed trailers the most common method of attachment is welding. Welding is economical as it saves time, materials and weight.
Typically, a spring hanger in the shape of an upside-down U is welded to the lower flange of a frame member, such as a longitudinal i-beam or other rail, so that two spaced apart, substantially parallel plates extend downward. Springs and other suspension components are secured to openings provided in the plates.
As trailer design and manufacturing capabilities have improved, the use of higher strength steel in the support beams has allowed for greater stress and strain in the beam and specifically in the flange to which suspension components are attached. This stress is transferred to the suspension brackets and associated welds. The most highly stressed and critical part of the beam is the bottom flange.
Higher strength steel necessitates more critical weld procedures, and as such is more sensitive to deviations from these procedures. In spread axle and multi-axle configurations, front spring hangers in particular need to be attached to the beam in a relatively forward position, where the stresses on the beam are higher as compared to the rear. In dynamic loading situations, such as those experienced by a moving trailer, cyclical stress occurs which can in turn lead to metal fatigue or failure. Specifically, by welding a bracket such as a spring hanger to the bottom flange of the beam, an abrupt change in the beam structure occurs. This results in localized high stress and accelerated fatigue.
A need exists for an improved spring hanger and method of attachment permitting the hanger to be attached to, and thus transferring the suspension forces to, a part of the beam structure such as the web that is not as highly stressed. While optimal location can be determined by stress analysis, the preferred point of attachments is on the web, roughly midway between the top of the beam and the bottom flange.